Switching from metal components to resin components has recently been actively studied for the purposes of weight saving and cost reduction. The studies have led to practical use of vehicle components, industrial components, and electrical and electronic components formed using a thermoplastic resin such as a polyamide resin, a polycarbonate resin, and a polyacetal resin. Also for use as sliding members including gears and bearing retainers, metal sliding members have been more and more replaced by resin sliding members. These thermoplastic resins, however, are insufficient in sliding properties, as the sliding members are used under high load, high temperature, and high-speed rotation conditions. Thermoplastic resins therefore may cause problems such as wear, fusion, cracking, and chipping.
Meanwhile, fluororesins are excellent in sliding properties, heat resistance, chemical resistance, solvent resistance, weather resistance, flexibility, electrical properties, and other properties, and are thus used in a variety of fields including cars, industrial machines, OA equipment, and electrical and electronic equipment. Particularly, fluororesins have excellent sliding properties, and are one of the resins having a notably low friction coefficient. Fluororesins, however, have inferior mechanical properties and physical heat resistance represented by deflection temperature under load, compared to crystalline heat-resistant thermoplastic resins in many cases. Also, in some cases, fluororesins have inferior dimensional stability compared to amorphous heat-resistant thermoplastic resins. Hence, the range of use of fluororesins has been limited.
Accordingly, thermoplastic resins have been studied for the purpose of improving their sliding properties and applying them to sliding members in wider fields. For example, Patent Literature 1 discloses a resin composition containing 1 to 50 parts by weight in total of a fluororesin and graphite for each 100 parts by weight of a resin composition that consists of 60 to 99 parts by weight of a thermoplastic resin having a heat deformation temperature of 100° C. or higher and 40 to 1 part by weight of carbon fibers. Patent Literature 2 discloses a resin composition containing a thermoplastic resin (A) having a molding temperature of 300° C. or higher, and a polymer (B) obtained by polymerization of an essential component of fluoroacryl α-fluoroacrylate that has a specific structure.
Fluororesins are also known to be added to a thermoplastic resin for purposes other than improvement of the sliding properties. For example, Patent Literature 3 discloses a technique of improving the mold-processability, including decreasing the extrusion pressure and extrusion torque, in the mold-processing of engineering plastics. The technique includes adding 0.005 to 1% by mass of a fluoropolymer based on the total mass of the engineering plastics and the fluoropolymer. Patent Literature 4 discloses a technique of mixing PEEK resin fine powder in a water dispersion of a PFA resin at a PFA:PEEK weight ratio of 75:25 to 70:30, directly applying the dispersion to a roughened metal surface in accordance with common methods, and baking the resulting product, so that a PFA-PEEK compound coating film having adhesion durability is formed.
Polyether ether ketone (PEEK) resin has comparatively favorable sliding properties among the thermoplastic resins, and thus has been put into practical use for sliding members such as a gear and a bearing retainer. The sliding properties, however, are not sufficient under severe sliding conditions such as high load. To improve the sliding properties of PEEK, PEEK compositions containing PTFE powder were developed and are available. The PEEK compositions containing PTFE powder indeed have a decreased coefficient of kinetic friction, but have low sliding properties which are represented by a limiting PV value. For this reason, the sliding properties are desired to be further improved.